In recent years, fuel saving characteristics of vehicles are again regarded as important, as the global environmental issues are drawing more attention. As for the global environmental issues, measures need to be promptly taken against global warming. Thus, improvements to enhance fuel-saving performance have repeatedly been made for vehicles with engines that emit greenhouse gases such as carbon dioxide to reduce emissions of greenhouse gases through improvement of fuel efficiency.
However, no matter how high the original fuel saving characteristics of the vehicle are, if a driver's driving manner is against fuel saving, for example, if the driver pushes the accelerator excessively for acceleration, wasteful fuel consumption is caused by an excessive accelerator operation, making high fuel saving characteristics of the vehicle meaningless. Thus, various techniques have conventionally been proposed for notifying the driver when a predetermined acceleration threshold is exceeded or a predetermined accelerator opening threshold is exceeded so as to make the accelerator operation during driving by the driver more contributive to fuel-saving, even if the contribution is small.
According to a conventional technique, for example, a fuel-saving warning is issued when the accelerator opening exceeds a permissible range of the driver's behavior pattern defined in advance based on a three-dimensional curve showing relationships among the accelerator opening by a driving operation, speed of engine revolution, and fuel consumption. Accordingly, excessive accelerator operations can be suppressed.